We are continuing our work on humoral and cell-mediated immune reactions to human tumor-associated antigens. A major effort at this time goes into using the monoclonal antibody technique to detect and characterize cell surface antigens of various human tumors, particularly melanomas. So far, antigens of very restricted distribution, as well as antigens shared by many tumors, have been detected. A particularly interesting antigen, p97, has been demonstrated in about 90% of human melanomas and about 50% of other human tumors, but has not, so far, been detected in normal human tissues. We are attempting to develop radioimmunoassays for this antigen, to study its distribution further, to investigate to what extent it is expressed in vivo, whether it can undergo antigenic modulation, and whether a p97 positive tumor gives rise to variants which lack p97. Similar studies are being conducted with p210, another human tumor-associated antigen, which we recently identified; p210, has, so far, been less studied for specificity. Several other hybridomas forming antibodies reacting with cell surface components of human tumor cells, are presently being worked up. The relationship, if any, between antigens detected by the hybridoma technique, such as p97, and antigens recognized by the patients (in the form of targets for humoral or cell-mediated reactivity) will be investigated, using various blocking assays. Other studies concern the targets of cell-mediated immune responses of Moloney virus-induced sarcomas, as outlined in my original grant application.